Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity.
In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Once the catheter is positioned within the heart, the location of aberrant electrical activity within the heart is then located.
One location technique involves an electrophysiology mapping procedure whereby the electrical signals emanating from the conductive endocardial tissues are systematically monitored and a map is created of those signals. By analyzing that map, the physician can identify the interfering electrical pathway. A conventional method for mapping the electrical signals from conductive heart tissue is to percutaneously introduce an electrophysiology catheter (electrode catheter) having mapping electrodes mounted on its distal extremity. The catheter is maneuvered to place these electrodes in contact with the endocardium. By monitoring the electrical signals at the endocardium, aberrant conductive tissue sites responsible for the arrhythmia can be pinpointed.
For sensing by ring electrodes mounted on a catheter, lead wires transmitting signals from the ring electrodes are electrically connected to a suitable connector in the distal end of the catheter control handle, which is electrically connected to an ECG monitoring system and/or a suitable 3-D electrophysiology (EP) mapping system, for example, CARTO, CARTO XP or CARTO 3, available from Biosense Webster, Inc. of Irwindale, Calif.
Regardless of the size and number of the ring electrodes, ring electrode pairs are evenly spaced along the catheter. The closely-spaced electrode pairs allow for more accurate detection of near-field potentials versus far-field signals, which can be very important when trying to treat specific areas of the heart. For example, near-field pulmonary vein potentials are smaller/weaker signals whereas the atria, located very close to the pulmonary vein, provides much larger/stronger signals. Accordingly, even when the catheter is placed in the region of a pulmonary vein, it can be difficult for the electrophysiologist to determine whether the signal is a small, close potential (from the pulmonary vein) or a larger, farther potential (from the atria). Closely-spaced bipoles permit the physician to more accurately determine whether he is looking at a close signal or a far signal. Accordingly, by having closely-spaced electrodes, one is able to target exactly the locations of myocardial tissue that have pulmonary vein potentials and therefore allows the clinician to deliver therapy to the specific tissue. Moreover, the closely-spaced electrodes allow the physician to determine the exact anatomical location of the ostium/ostia by the electrical signal.
However, manufacturing and assembling catheters with closely and precisely spaced ring electrodes pose many challenges. Where desired spacing between electrode pairs range on the order of millimeters or even microns, accuracy and consistency in spacing become critical to catheter manufacturing and assembly. Conventional methods often use adhesives such as polyurethane to seal each ring electrode, which creates a margin between adjacent electrode or electrode pairs that limits how closely the electrodes can be spaced from each other. Spacing of 1.0 mm or larger between electrode pairs can be achieved using such conventional methods. However, spacing smaller, especially 0.2 or 0.1 mm spacing is difficult to achieve. At such smaller spacing, there is the risk of two electrodes in contact due to electrode tolerance specification or shifting of electrodes during assembly when medical grade adhesive such as Polyurethane is applied or when medical epoxy is curing.
Moreover, the conventional methods of attaching a lead wire to a ring electrode also typically require spacing tolerances between adjacent ring electrodes. Such attachment methods often result in an acute angle at which the lead wire must extend to reach the ring electrode which can stress the lead wire and result in detachment or breakage.
Accordingly, a need exists for an electrophysiology catheter with a ring electrode configuration that provides very closely spaced electrodes with minimized stress and strain to attached lead wires. There is also a need for a method of manufacture and assembly of such a catheter wherein very close spacing between electrodes can be achieved readily and consistently with improved precision and accuracy.